The invention relates to a method for transporting and installing an expandable steel tubular.
An expandable slotted steel tubular is known from European patent specification EP 0643795 and an expandable unslotted or solid tubular made of a formable steel grade is known from International patent application, publication No. WO 98/00626.
These prior art references disclose that an essentially conical mandrel may be used to plastically expand the tubular such that the internal and outer diameter of the tubular are increased.
A general problem with these and other known steel tubulars is that they are voluminous and fragile elongate pieces of equipment which are difficult to transport from a manufacturing plant to a use site, which results in high transportation and storage costs. Furthermore, a large amount of connectors is required to make up a tubular string.
It is an object of the present invention to provide a method, which allows a cheap and efficient transport of expandable steel tubulars from a manufacturing plant to an industrial site where the tubular is to be expanded and used.
It is observed that it is known from U.S. Pat. No. 3,811,633 to make an extendable tubular structure, which is collapsibly folded when wound onto a spool for storage. The known structure thereto comprises a pair of parallel elongated ribbons which are interconnected by profiled side walls which are folded flat during storage and which are folded out when the tubular is unwound such that a generally square tubular is formed which is neither cylindrical nor expandable.
It is observed that is also known in the art to roll hoses that are used e.g. for domestic use or for fire fighting in a flat shape around a reeling drum or in a coil. However, such hoses are made of plastic fabric and/or elastomeric materials which are by their nature already flexible so that flattening can be easily achieved, whereas flattening of steel tubulars for industrial use has not yet been applied.
Therefore, when used in this specification, the term steel tubular excludes an essentially flexible non-metallic hose which is not installed, but used in a movable mode e.g. for domestic, gardening or fire fighting applications.
It is observed that U.S. Pat. No. 3,934,660 discloses a method for in-situ forming a well casing wherein a resilient metal strip is folded into a scrolled shape and maintained in that shape by explosive bolts whereupon the folded casing is inserted into the well. The casing is then installed by releasing the bolts such that the casing unscrolls and presses itself against the borehole wall.
The method for transporting and installing a steel tubular in accordance with the pre-amble of claim 1 is known from International patent application WO98/07957. In the known method a tubular steel casing is reeled in a collapsed flattened configuration around a reeling drum. The flattened casing is after unreeling from the drum and before inserting the casing into a borehole further folded into a kidney shape to permit movement of the flattened casing through the borehole. When the folded and flattened kidney-shaped casing has arrived at the downhole location where it is to be installed the kidney-shaped casing is inflated into a cylindrical shape whereupon an inflatable packer may be inserted into the casing to plastically deform a portion of the upper part of the casing into tight gripping and sealing engagement with an already installed casing section.
The folding of the flattened casing into a kidney shape involves high stresses and if the casing is moved through a curved section of the borehole the casing is bent even further which can easily lead to buckling or rupture of the casing.
The present invention aims to overcome the problems associated with the prior art installation techniques and to provide an installation method which neither requires the folding of the casing into a kidney-shape during installation nor requires the use of a metal strip which unscrolls itself against the borehole or other cavity wall.
The method according to the invention is characterized in that before the tubular is positioned at the site where it is to be installed the tubular is first unflattened into a substantially cylindrical or oval shape and that the thus already unflattened tubular is radially expanded along at least a substantial part of its length after the tubular has been positioned at the site where the tubular is to be installed.
It is observed that surprisingly it has been found that the plastic properties that are required to make steel tubulars sufficiently flexible to make them expandable can also be used to flatten the unexpanded tubular during transport and to unflatten the tubular at the site where it is to be used.
It will be understood that the transport of flattened unexpanded steel tubulars significantly reduces the volume of the transported tubulars and associated transport costs.
Preferably the flattened unexpanded tubular is wound around a reeling drum before transporting the tubular to the site where it is to be used and reeled from the reeling drum before unflattening the tubular.
Suitably the tubular is made of a formable steel grade and/or comprises a predetermined pattern of openings or weak spots which open up and are deformed during the expansion process.
Preferably said pattern is such that at opposite sides along the circumference of the tubular a longitudinal or helical series of openings or weak spots is arranged which series define a longitudinal or helical band where the tubular wall is folded during the step of flattering the unexpanded tubular.
A suitable tubular of the above kind comprises a staggered pattern of elongate slots or elongate weak areas which open up into a substantially prismatic shape during the expansion process. Such an expandable slotted tubular is disclosed in European patent specification EP 0643795. It is observed that when used in this specification the term flattening of a tubular means that the tubular is deformed into a truly flat or substantially oval shape and that the term unflattening of a tubular means that the roundness of the tubular is increased, so that the tubular obtains a substantially cylindrical or oval shape.
Experiments have shown that an expandable steel tubular which is equipped with a staggered pattern of partially overlapping axial slots can be flattened such that the opposite tubular walls touch each other when the flattened unexpanded tubular is wound around a reeling drum and that subsequently the unexpanded tubular can be unflattened into a nearly cylindrical shape.
Since if the unflattened tubular is inserted into a cavity, such as a borehole or corroded pipe, that cavity is oversized when compared with the outer diameter of the unexpanded tubular there is no requirement to bring the unexpanded tubular into a perfectly cylindrical shape. Also the expansion of the tubular with e.g. a conical expansion mandrel does not require the use of a perfectly cylindrical unexpanded tubular as a starting point, whereas the conical mandrel will still be able to expand the tubular into a substantially cylindrical shape.
Expandable solid tubulars made of a formable steel grade preferably are flattened into a substantially oval shape when they are reeled around a reeling drum, whereas the roundness of the unexpanded tubular is increased before the expansion process. Again expansion of the tubular using an expansion cone still resulted in a substantially cylindrical expanded tubular.
Thus it will be understood that flattening of expandable tubulars significantly reduces transport and storage cost since the storage of tubulars which are both unexpanded and flattened has synergetic effects, whereas the temporary flattening during transport and storage has no effect on the roundness of the expanded tubular.
It is preferred that the tubular is unflattened by moving the flattened unexpanded tubular in a longitudinal direction through a funnel arrangement which comprises a tubular opening formed by series of rollers and/or a tubular guide funnel, which opening has an inner diameter which is substantially equal to the outer diameter of the unexpanded unflattened tubular.
The method according to the present invention is very suitable for use with expandable tubulars which are made of a formable steel grade and are in use inserted into an underground wellbore or corroded pipe and then expanded to form a steel lining in the wellbore or existing pipe.
When used in this specification the term formable steel grade means that the steel is subject to substantial strain hardening as a result of the expansion process. Preferably the tubular is made of a high strength steel grade with formability and having a yield strength-tensile strength ratio which is lower than 0.8 and a yield strength of at least 275 MPa. Suitable steels of this kind are dual phase (DP) high strength, low alloy (HSLA) steels having a strain hardening exponent n of at least 0.6, and preferably at least 0.16.
If the tubular is to be inserted into a tubular cavity, such as a wellbore or subsurface or above-ground pipeline, and to be moved in a centralised position through the cavity then the tubular may be equipped with a series of bow spring centralisers which are at least one end slidably secured to the outer surface of the tubular and which centralisers are also flattened when the unexpanded tubular is flattened and which deform into a low shape when the tubular is unflattened.
If the tubular is slotted and to be used in an area where an impermeable tubular wall is required then an impermeable wrapping or elastomeric sleeve may be arranged around the tubular to provide a fluid seal.
Suitably the tubular is expanded by an expandable expansion mandrel which is inserted into the unexpanded unflattened tubular in its retracted shape and subsequently expanded and moved in an axial direction through the tubular during the tube expansion process.